The protection of crops from weeds and other undesired vegetation that inhibits crop growth is a constantly recurring problem in agriculture, horticulture and other plant cultivation practices. To help combat this problem, researchers in the field of synthetic chemistry have produced an extensive variety of chemicals and chemical formulations effective in the control of such unwanted growth. Chemical herbicides of many types have been disclosed in the literature and a large number are in commercial use. Commercial herbicides and some that are still in development are described in The Pesticide Manual, 13th Edition, published 2003 by the British Crop Protection Council.
Many herbicides also damage crop plants. The control of weeds in a growing crop therefore requires the use of so-called ‘selective’ herbicides, which are chosen to kill the weeds while leaving the crop undamaged. In practice, few herbicides are fully selective, in that they will kill all the weeds and leave the crop untouched at a particular application rate. The use of most selective herbicides is actually a balance between applying enough herbicides to acceptably control most of the weeds and causing only minimal crop damage.
Herbicides may be formulated as wettable powders, water dispersible granules, suspension concentrates, emulsifiable concentrates, powders or dusts, flowables, solutions, suspensions, controlled release forms such as microcapsules, or as dry spreadable or broadcast granules. Herbicides can be co-formulated with other pesticides such as other herbicides, insecticides or fungicides. The choice of formulation type can be influenced by the mode of application. Both formulation type and mode of action for any given selective herbicide may affect both its activity and selectivity. Accordingly, the optimum formulation for any particular selective herbicide will depend upon the mode of application and nature of the plants and any other pests to be controlled.
For certain agricultural, horticultural, and other pest control applications it is often desirable to formulate pesticides as dry spreadable or broadcast granules, as opposed to wettable powders or water dispersible granules that are designed for admixing in large volumes of water such as tank mixes and ultimately sprayed upon sites to be treated. The challenge to deliver chemically stable products for these two approaches can be different.
Selective herbicides formulated as dry spreadable granules are important commercial products because of their ability to eliminate undesirable vegetation in large areas of cultivated vegetation and their ease of application, either by hand or a mechanical means. For example, a practical and labor-saving approach to selective herbicide delivery in areas such as golf courses, parks, lawns, gardens and woodlands has been broadcast application of granular herbicide products via rotary spreader.
Broadcast granular herbicides can be a selective herbicide applied to an inert material, like clay, peanut hull or ground corn cobs, or can be a combination fertilizer/herbicide, wherein the selective herbicide is applied to a fertilizer material, i.e., a “weed and feed” composition.
In a granular form, a selective herbicide is impregnated into, absorbed or coated onto an inert granular carrier or a granular fertilizer material. The granular herbicide product is supplied in a plastic bag, a plastic drum, or a fiber keg. The granular herbicide product is applied to vegetation by directly spreading herbicide granules onto the vegetation at a suitable dosage rate.
One important class of selective herbicides is the triketone class which includes those compounds disclosed, inter alia, in U.S. Pat. Nos. 4,780,127, 4,938,796, 5,006,158 and 5,089,046 the disclosures of which are incorporated herein by reference. One known triketone herbicide is 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione. A challenge that is seen with 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione, when used in the acid form, is chemical stabilization in certain environments, in a liquid state, in a liquid state applied on or to a solid carrier and on or in a solid carrier. Granule formulations containing the acid form of 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione are known (University of Maryland Department of Natural Resource Science and Landscape Architecture: Turfgrass Pathology, Weed Science and Physiology Research Summaries (2005), p. 19).
In addition to the acid form, another known form of 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione is as a metal chelate, for example a copper chelate. These metal chelates are disclosed, inter alia, in U.S. Pat. No. 5,912,207 (the disclosure of which is incorporated herein by reference) where they are shown to have unexpectedly superior stability in certain environments when compared to unchelated 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione. The '207 patent addresses stabilization of products to be diluted and applied as liquids. Stabilization of chelated 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione formulated in a solid form for spreadable application (as opposed to liquid application) is not specifically disclosed in the '207 patent. Stabilising a cyclohexanedione a solid substrate is different to stabilising it in a liquid medium, because it is necessary to block the surface interaction between the reactive granule and the compound itself.
There is a need to develop granular 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione compositions with improved stability on long term storage. The present invention provides such stabilized granular 2-(2′-nitro-4′-methylsulphonylbenzoyl)-1,3-cyclohexanedione compositions.